1. Field of the Invention
The present invention relates, in general, to electric power service to homes and buildings and, more specifically, to overvoltage and/or overcurrent devices used with watthour meters mounted in watthour meter sockets at homes and buildings.
2. Description of the Art
Electrical power is supplied to an individual site or service by external electrical power line conductors located above or below ground. In a conventional arrangement, electrical power line conductors are connected to contacts in a watthour meter socket mounted on a building wall. Electrical load conductors are connected to another set of contacts in the meter socket and extend to the electrical distribution network in the building. A watthour meter is connected into the contacts in the meter socket to measure the electric power drawn through the load conductors.
Due to the current trend toward the use of plug-in watthour meters, A to S type socket adapters have been devised which convert A-base type bottom connected watthour meter sockets to receive plug-in watthour meters. Another type of socket adapter has been devised which allows the installation of other devices between the watthour meter socket and a plug-in watthour meter.
Such watthour meter socket adapters have also been provided with power disconnect devices, such as circuit breakers or ground fault circuit interrupters, both for protecting the electrical service as well as, in certain applications, to limit the amount of power supplied to the site. Such power disconnect devices may include an elongated plunger, the end of which extends outwardly through an opening in the annular side wall of the socket adapter when the circuit breaker is in the open or power disconnected position. The exposed end of the plunger can be pushed through the side wall of the watthour meter socket adapter to close the circuit breaker and to reapply power to the site. In certain of these devices, the ends of the plungers extending through the sidewall of the adapter have been colored red for high visibility of a tripped or open condition of the circuit breaker, etc.
Many older homes and buildings, even where originally wired with bottom connected watthour meters, have been converted by electrical utilities to socket style meters by the use of the above-described A to S socket adapter. This type of socket adapter does not require the existing wires to be moved which could cause the insulation which has become brittle with age to fall apart exposing the conductor. If this happens, the conductors and the socket itself need to be replaced which is a time consuming and costly process. This also creates further problems since the service entrance cables into the building should also be replaced and so on down the line through the distribution network as individual conductors are moved.
Currently, homes and buildings often have various electrically powered devices, such as a large number of appliances, computers, medical systems, video display systems, etc., which were not envisioned when the original distribution network conductors were sized to meet a particular maximum load at the time of the original installation. Older homes and buildings have been wired with smaller gauge wires, as small as #12 AWG, with up to and including #6 AWG also being common. The amperage usage in many of these systems exceeds the safe capacity of the individual wires or conductors. Further, due to the age of such wiring installations, the insulation on the individual wires typically is brittle and any movement of the wires for service upgrade could lead to the aforementioned deterioration or separation of the insulation from the wires which could lead to arcing between adjacent conductive elements and electrical fires.
One method to reduce fires in older installations where the insulation on the system wires is deteriorating is to prevent the system voltage levels from becoming too high and arcing. A socket type watthour meter has built-in surge air gaps will generally arc across the gaps at about 2,500 to 5,000 volts in the event of a voltage surge or transient thereby protecting the wiring system up to this voltage level. However, surge or transient voltages less than this level can often cause arcing between the building wires where the wire insulation has deteriorated. Once arcing begins, the arc itself can eventually form a conductive path and fault thereby creating a potential fire hazard. Of course, it is also important that voltage surges and transients be blocked from the distribution system to protect the electrical appliances and electronic devices attached thereto.
To address this problem, current limiting fuses and circuit breakers have been connected by wires between the load jaw contacts and load blade terminals in the socket adapter to create an open circuit at excessive amperage levels. Other surge voltage limiting devices have been connected between the line jaw contacts or blade terminals and ground to shunt voltage surges and transients to ground before such excessive voltages reach the watthour meter or load distribution network.
One such watthour meter base surge suppression system is disclosed in U.S. Pat. No. 5,023,747. In this device, a pair of surge suppressors in the form of metal oxide varistors are each connected to an electrical contact element which is in turn connected to the jaw contacts of a watthour meter socket. Voltage surges present on the blade terminals are conducted via the metal oxide varistors to respective fuses in the form of fusible links and then to ground to prevent the surges from being transmitted through the watthour meter and onto the electrical load distribution network. This surge suppression system also includes a diagnostic circuit which couples the varistors to an audible signal generator, such as a buzzer, which indicates that one of the fusible links has ruptured upon the occurrence of a line surge.
Such surge suppression systems have also been proposed with a visual indication that one of the fusible links or MOVs has opened due to the occurrence of a line surge. However, the surge suppression elements are mounted within the interior of a watthour meter socket adapter or socket and not visible exteriorly of the socket or socket adapter due to the need to sealingly enclose the watthour meter in the socket in order to prevent contact with the high voltage in the socket or to prevent tampering with and/or theft of electric power from the socket. Thus, unless an individual is within the vicinity of the socket adapter to hear the audible sound generator, the occurrence of an open circuit in the surge suppression device due to a line surge is not likely to be detected. Further, after the surge has passed and voltage and current levels have returned to normal, there is no indication the exteriorly of the socket adapter that one or more of the surge suppression devices is open and thereby not providing any surge suppression protection for the meter socket.
Small neon lamps have been mounted on the sidewall of the adapter or surge to indicate a change in state of the surge suppression devices. However, such lamps are prone to breakage and could leave unsafe, broken or disconnected electrical wires in the housing.
Thus, it would be desirable to provide the watthour meter socket adapter having a provision for providing a signal indicative of the opening of a surge suppression device within the socket adapter. It would also be desirable to provide the watthour meter socket adapter which provides an external visual signal to indicate that one or more of the surge suppression devices within the socket adapter has opened.
The present invention is an electrical service apparatus having surge suppression protection.
The electrical service apparatus, such as a watthour meter socket adapter, includes a housing having a hollow interior. A plurality of line and load jaw contacts are mounted in the housing for receiving the line and load blade terminals of a watthour meter. A plurality of line and load blade terminals are also mounted in the housing and extend outward from the housing for insertion into electrical connection with jaw contacts in a watthour meter socket. Surge suppression means are mounted in the housing and coupled between ground potential and the line and load jaw contacts or blade terminals for conducting electrical surges and transients to ground.
In a preferred embodiment, the housing includes a base with a central wall. The line and load blade terminals and jaw contacts are mounted in the central wall of the base.
Unique insulating brackets or barriers are carried on the central wall of the base and surround each jaw contact. The barriers interact with flange and edge portions of each jaw contact to securely position each jaw contact in the base, with the jaw contact portion disposed interiorly within the socket adapter in position for receiving a blade terminal of a watthour meter, and the blade terminal extending through the base exteriorly of the rear wall of the base for insertion into jaw contacts in a watthour meter socket.
The surge suppression means is mounted on the central wall of the base. Preferably, the surge suppression means comprises a plurality of metal oxide varistors, each of which is connected to one of the load blade terminals and ground potential.
The surge suppression elements are mounted on a circuit board having a predetermined peripheral edge configuration. The peripheral edge configuration is disposed between the barriers on the central base wall for positioning and supporting the circuit board in position between the jaw contacts in the base.
In one aspect of the invention, the peripheral edge configuration of the circuit board has a T-shape with a short leg extending generally centrally of an elongated stem carrying the surge suppression elements or metal oxide varistors. The stem is designed to fit between certain of the insulating barriers to position the circuit board laterally on the base and the leg is disposed between other barriers to position the circuit board longitudinally on the base.
In another aspect, the short leg on the circuit board may be eliminated such that the circuit board has a generally rectangular configuration disposable centrally on the base between spaced portions of the insulated barriers. A mounting screw also used to attach a ground wire to the circuit board may be inserted through the circuit board into the base to secure the circuit board to the base.
According to a unique feature of the present invention, a signal generating means, such as a switch or a relay having a switchable contact, is energized by a signal generated by the surge suppression elements and/or circuit to indicate that one of the surge suppression devices has opened. Activation of the relay either closes a normally open contact or opens a normally closed contact to send a signal to a signal receiving remote circuit, such as to automatic meter reading equipment which may be mounted internally or externally of the socket adapter or an alarm or buzzer in the adjacent building. This signal may be reported by the automatic meter reading equipment to its central host system to provide a utility or to provide an indication in the building that at least one of the surge suppression elements in a particular metered site has opened.
In another aspect of the present invention, an insulating shield is disposed over the jaw contacts and includes apertures alignable with the jaw contacts in the housing to allow the blade terminals of a watthour meter to pass therethrough into contact with the jaw contact; while enclosing the jaw contacts to prevent inadvertent contact by a utility service person. The safety shield uniquely includes a unique light transmitting means or guide integrally carried on the shield which has a first end positioned adjacent to the visible light generating device, such as at least one LED, on the surge suppression circuit board to transmit the light generated by the LED, indicating the state of at least one of the surge suppression devices to an opposed second end which is positioned relative to the sidewall of the socket adapter housing to be visible exteriorly of the socket adapter housing. Preferably, the second end of the light transmitting means or guide is disposed through or viewable through an aperture in the sidewall of the housing so as to be readily visible exteriorly of the housing. A seal carried on the light guide seals the aperture in the sidewall of the housing.
The watthour meter socket adapter with surge suppression protection according to the present invention provides several advantages and improvements over previously devised watthour meter socket adapters carrying surge suppression circuits.
First, the insulating barriers disposed adjacent to each of the jaw contacts in the socket adapter housing serve a dual function which, in addition to locating and positioning the jaw contacts on the base, are also disposed in engagement with the peripheral edge of the surge suppression circuit board to position and locate the circuit board on the base.
The provision of a signal generator, such as a relay, which is activated by the signal generated by the surge suppression circuit when one of the surge suppression elements changes state, is uniquely employed to provide an external signal, such as to automatic meter reading equipment, to provide an indication to the utility that at least one of the surge suppression elements in a particular meter site has changed state.
Finally, the use of a light transmitting means or guide on the safety shield enables the light generator or LED, which is activated when the change of state of at least one of the surge suppression devices, to be viewed exteriorly of the socket adapter. This prevents a prior art externally mounted surge suppression device state indicator from being broken and exposing unsafe electrical wires.